1. Field of the Invention
The present invention relates to pressure regulators and more particularly to a pressure regulator valve assembly for regulating the absolute pressure of a fluid source.
2. Description of the Related Art
In operating a cryogenically cooled sensor in an aircraft, the sensor temperature must be held fixed, independent of the ambient pressure. If the cooling is provided by a cryogen reservoir, this typically implies that the absolute pressure in the reservoir be held within a narrow range in the neighborhood of an ideal value. Similar problems may occur in chemical processing, where the pressure within one vessel must be held fixed; independent of the pressure in the region to which fluids are exhausted, or from which they are supplied. Existing mechanical (nonelectrical) pressure regulators are generally differential and not absolute, and they regulate downstream pressure.
Examples of pressure regulators that control downstream pressure include U.S. Pat. No. 2,766,593, issued to O. Mitchell et al.; U.S. Pat. No. 3,709,242, issued to Charles P. Chase; and, U.S. Pat. No. 5,694,975, issued to Paul G. Eidsmore.
U.S. Pat. No. 5,692,379, issued to J. R. Gallivan et al.; and, U.S. Pat. No. 5,564,278, issued to J. R. Gallivan, disclose long-term thermally stable cryostats.
U.S. Pat. No. 4,709,575, issued to W. P. Myers, discloses an absolute pressure regulator containing an "aneroid". The Myers regulator utilizes the pressure differential of two gases to regulate flow.
U.S. Pat. No. 5,394,900, issued to S. Okuyama et al., discloses a pressure regulating valve in which a resinous bellows expands and contracts in the axial direction in accordance with the pressure fluid. This causes a valve body retained in the bottom portion of the bellows by means of a valve body retaining member to come in contact with and separate from a valve seat to thereby regulate the outflow of fluid, where the resultant fluid pressure can be regulated to a desired pressure.
None of the aforementioned devices regulates upstream pressure and provide for a vacuum reference and a bias for adjusting the pressure.